The present invention relates to protective covers for fasteners, and in particular, to covers for the exposed ends of large bolts and nuts found, for example, on the bases of wind turbine towers.
Wind turbine towers, which can be as tall as 250 feet, must withstand tremendous forces without excessive flexing, settling, or other movement which would impair the safe operation of the generator perched at the top. They are typically secured to concrete piers sunk into the ground, by threaded bolts which extend upward from those piers and through holes in a mounting flange found at the bottom of the tower. This mounting technique is both secure and reversible, allowing for relatively simple removal of damaged or obsolete towers.
To secure the benefit of reversibility, the bolts and their associated nuts and washers must be protected from the corrosion that comes from exposure to the weather. One means of doing this is to cover them with plastic shells designed to keep out the weather. Such shells include, for example, those of Tooman, U.S. Pat. No. 6,808,350. The Tooman shell remains held in place by gripping a nut tightly on all sides. In use, this shell has posed two practical problems. First, the Tooman shell is intolerant of errors during the assembly process. It cannot easily accommodate washers which are oversized or off-center, nor seal properly if more than one washer is used. This requires workers to use great care during assembly, given that errors are difficult to correct once the nuts have been fully tightened. Second, the close fit between the nut and the shell tends to create a capillary action which draws water into the shell. This effect is enhanced by cyclic changes in internal pressure caused by temperature and sun exposure variations during the day. Water in the shell leads to corrosion.
What is needed, then, is a device for the protection of nuts and bolts which is easily installed, is held firmly in place without causing capillary action, and is capable of accommodating minor variations in the fasteners to be protected.